Pneumatic tire

ABSTRACT

A pneumatic tire comprises a cord-reinforced layer such as carcass, belt, bead reinforcing layer which is made of metallic cords, each metallic cord is made up of six to twelve metallic filaments whose diameter is in a range of from 0.15 to 0.45 mm, the metallic filaments include waved filaments and unwaved filaments, each waved filament is two-dimensionally waved at a wave pitch and wave height before twisted, the wave pitch is in a range of from 5.0 to 35.0 times the diameter of the filament, and the wave height is in a range of from 0.2 to 4.0 times the diameter of the filament, and the metallic filaments are twisted together into the cord at a twist pitch of from 10 to 40 mm so that the two-dimensionally waved filaments are each subjected to a certain rotation around its axial.

PNEUMATIC TIRE

The present invention relates to a pneumatic tire reinforced by metalliccords, more particularly to an improved metallic cord in which rubberpenetration is improved without being increased in the cord diameter.

In the pneumatic tires especially radial tires for trucks, buses, lighttrucks and the like, steel cords are widely used as reinforcing cordsfor the carcass, belt, bead reinforcing layers and the like.

In recent years, in order to improve rubber penetration into such asteel cord, an invention was made, which is to use a waved filament inmaking a steel cord.

Generally, in the process of making a steel cord, as well known in thetire cord art, in order to prevent twisted filaments from loosing, thesteel filaments are twisted together in a direction while giving eachfilament a rotation around its axis which rotation is reverse to thetwist direction and the degree of the rotation is the same as the twist.In the finished cord, accordingly, each filament is not subjected to arotation around its axis.

In such a conventional twisting method, if a waved filament is used, itis necessary to wave steel filaments largely in order to improve rubberpenetration.

When steel filaments are waved largely, it is inevitable that thediameter of the finished cord increases and the initial elongation ofthe finished cord under light loads increases. As a result, thethickness and weight of cord-reinforced layers are increased and furtherthe reinforcing effect tends to decrease.

It is an object of the present invention to provide a pneumatic tirewith a cord-reinforced layer such as carcass, belt, bead reinforcinglayer and the like of which metallic cords are improve in the rubberpenetration without increasing the cord diameter.

According to the present invention, a pneumatic tire comprises acord-reinforced layer made of metallic cords,

each of the metallic cords being made up of six to twelve metallicfilaments whose diameter (d) is in a range of from 0.15 to 0.45 mm,

the six to twelve metallic filaments including waved filaments andunwaved filaments,

each of the waved filaments being two-dimensionally waved at a wavepitch Pw and wave height (h) before twisted, the wave pitch Pw being ina range of from 5.0 to 35.0 times the diameter (d) of the filament, andthe wave height (h) being in a range of from 0.2 to 4.0 times thediameter (d) of the filament,

the metallic filaments being twisted together into the cord at a twistpitch Pc of from 10 to 40 mm so that the two-dimensionally wavedfilaments are each subjected to a certain rotation around its axial.

Therefore, until the cord is rubberized, the two-dimensionally wavedfilaments become unstable, and gaps which effectively work on rubberpenetration can be formed between the filaments without increasing thethickness of the finished cord.

Embodiments of the present invention will now be described in detail inconjunction with the accompanying drawings.

FIG. 1 is a cross sectional view of a tire according to the presentinvention.

FIG. 2 is a schematic perspective view of a twisted of a waved filamentand unwaved filament.

FIG. 3 is a diagram showing the twisting of a metallic cord.

FIG. 4 is a schematic view of an example of the waved filament forexplaining the wave pitch and height.

FIG. 5 is a schematic cross sectional view of an example of the carcasscord showing an example of the filament arrangement.

FIGS. 6, 7 and 8 each show another example of the filament arrangementof the carcass cord.

FIG. 9 is a schematic cross sectional view of an example of the beltcord showing an example of the filament arrangement.

FIGS. 10 and 11 each show another example of the filament arrangement ofthe belt cord.

FIGS. 12 and 13 each show a schematic cross sectional view of an exampleof the belt cord showing an example of the filament arrangement.

FIG. 14 is a graph showing the cord strength and rubber penetration as afunction of a dXh/Pw value.

In the drawings, pneumatic radial tire 1 according to the presentinvention comprises a tread portion 2, a pair of sidewall portions 3 anda pair of bead portions 4 so as to form a toroidal shape, and the tireis provided with a carcass 6 extending between the bead portions 4, anda belt 7 disposed radially outside the carcass 6 in the tread portion 2.

The carcass 6 comprises at least one ply of cords arranged radially atan angle of from 70 to 90 degrees with respect to the tire equator andextending between the bead portions 4 through the tread portion 2 andsidewall portions 3 and turned up around the bead core 5 in each beadportion from the inside to the outside of the tire so as to form a pairof turnup portions 6 b and a main portion 6 a therebetween.

Between the main portion 6 a and turnup portion 6 b in each of the beadportion, there is disposed a rubber bead apex 8 extending radiallyoutwards from the bead core 5 and tapering towards its radially outerend.

The belt 7 comprises at least two cross plies of parallel cords laid atan angle of from about 15 to about 65 degrees with respect to the tireequator. In case of heavy duty tires, the belt 7 is usually composed ofthree or four plies. In case of light truck tires, the belt 7 is usuallycomposed of two or three plies. In case of passenger tires, the belt 7is usually composed of two plies.

Heavy Duty Radial Tire

FIG. 1 shows a heavy duty radial tire for trucks and buses as anembodiment of the present invention.

In this embodiment, each of the bead portion 4 is further provided witha bead reinforcing layer G. The bead reinforcing layer G in this exampleis disposed axially outside the carcass ply turnup portion 6 b and madeof rubberized metallic cords 10A laid crosswise to the adjacent carcassply cords.

The carcass 6 in this embodiment is composed of a single ply 6A ofmetallic cords 10C arranged radially at about 90 degrees.

The belt 7 in this embodiment comprises a radially innermost ply 7A ofrubberized parallel cords laid at an angle of from 35 to 65 degrees, andradially outer second, third and fourth plies 7B, 7C and 7D ofrubberized parallel cords laid at an angle of from 15 to 35 degrees. Inthe above-mentioned four plies 7A to 7D, at least two middle plies 7Band 7C which are cross plies in this example are made of metallic cords10. In this example, all the four plies are made of metallic cords 10B.

Carcass Cord

The metallic cord 10C for the carcass 6 is composed of seven to twelvemetallic filaments F whose diameter (d) is in a range of from 0.15 to0.30 mm, wherein the metallic filaments F are grouped into (i) bunches Bof two or three or four filaments or (ii) one filament F and bunches Bof two or three or four filaments, and they are twisted together at afinal twist pitch Pc of from 10 to 25 mm. The filaments F of each bunchB are twisted together into the bunch at a twist pitch Pf of from 3 to20 times the final twist pitch Pc. Further, the bunches B each includeat least one waved filament FA and at least one unwaved filament FB asshown in FIG. 2.

Hereinafter, each bunch and one filament F out of the bunches (in case(ii)) are generically called as “element”.

FIG. 3 is a diagram showing the twisting of the cord. A single bunch ofthe “elements” is rotated around its axis. This corresponding to thefinal twist (pitch=Pc). By this rotation, each element is essentiallysubjected to a rotation around the axis of the element which is in thesame direction and the same degree (Pc=Pf) as the above-mentionedrotation. In the metallic cord 10C, however, the degree of the rotationof each element especially bunch is decreased so that the twist pitch Pfbecomes 3 to 20 times the twist pitch Pc. Thus, the direction of thefirst twist for the bunches B is the same as the direction of the finaltwist for the cord. As a result, in the finished cord, the filaments,especially waved filaments are each subjected to a rotation around itsaxis which is in the same direction as the final twist but the degree ofrotation is less than the final twist. If the twist pitch Pf is lessthan 3 times or more than 20 times the final twist pitch Pc, the rubberpenetration deteriorates.

Incidentally, as the direction of the rotation of the waved filamentaround its axis in the finished cord, it may be reversed as far as itconcerned with the improvement in the rubber penetration.

Belt Cord

The metallic cord 10B for the belt 7 is composed of six to ten metallicfilaments F whose diameter (d) is larger than the carcass cord 10C andin a range of from 0.25 to 0.45 mm, wherein similarly to the carcasscord, the metallic filaments F are grouped into (i) bunches B of two orthree or four filaments or (ii) one filament F and bunches B of two orthree or four filaments, and they are twisted together at a final twistpitch Pc which is in a range of from 10 to 40 mm but usually limited toa range of not more than that of the carcass cord. Further, the bunchesB each include at least one waved filament FA and at least one unwavedfilament FB. The filaments F of each bunch B are twisted together intothe bunch at a twist pitch Pf of from 3 to 20 times the final twistpitch Pc.

The twisting in the belt cord 10B is made in the same way as the carcasscord 10C. Thus, the direction of the first twist for the bunches B isthe same as the direction of the final twist for the cord. The rotationof the waved filaments in the finished cord is in the same direction asthe final twist but the degree of rotation is less than the final twist.

Bead Reinforcing Cord

The metallic cord 10A for the bead reinforcing layer G is composed ofseven to twelve metallic filaments F whose diameter (d) is in a range offrom 0.17 to 0.25 mm.

The metallic filaments F include at least two waved filaments FA and atleast three unwaved filaments FB. The three or more of unwaved filamentsare necessary for decreasing the initial elongation of the cord underlight loads.

The twist structure thereof is rather different from the carcass cordand belt cord as explained later.

Waved Filament

In the drawings, the cross section of the waved filament FA is dotted,and the cross section of the unwaved filament FB is hatched, forconvenience sake, in order to distinguish from each other.

The waved filament FA is two-dimensionally waved at a wave pitch PW anda wave height (h) before being twisted.

FIG. 4 shows an example of the waved filament FA, wherein the waveformis a triangular waveform made up of straight segments 13 ofsubstantially the same length forming an obtuse angle therebetween.Also, a sawtooth waveform made up of alternate long straight segmentsand short straight segments and the like can be used. Further, A curvedwaveform devoid of straight segment such as sinusoidal waveform may beused. But, a waveform including straight segments 13 forming an obtuseangle therebetween is preferably used for the rubber penetration intothe finished cord.

As shown in FIG. 4, the above-mentioned wave height (h) is defined asthe peak-to-peak height of the wave, and the wave pitch Pw is defined asone cycle of the wave.

In case of carcass cord 10C and belt cord 10B, when the bunch B includestwo or more waved filaments FA, it is preferable that the wavedfilaments FA include at least two kinds of waved filaments FA which aredifferent from each other in respect of the wave pitch Pw. Thereby, therubber penetration into the cord can be improved although the waveheight (h) is relatively low. It may be possible to change the waveheights (h) between the different kinds of waved filaments FA. But, itis preferable not to largely change the wave heights (h), namely, thedifferent kinds of waved filaments FA have substantially the same waveheights (h) in order to avoid an excessive decrease of the cordstrength.

In case of bead reinforcing cord, however, it is preferable that all thewaved filaments FA have the same wave pitch Pw and the same wave height(h). If the waved filaments have different wave pitches Pw and differentwave heights (h), due to the twist structure mentioned later, a tensilestress concentrates on the shortest filament and the filament is liableto break because the filaments are very fine.

If the diameter (d) of the waved filament is less than 0.15 mm, the wavevanishes during twisting the waved filament and the rubber penetrationcan not be improved. Thus, the diameter of the waved filament should notbe less than 0.15 mm.

Carcass Cord Examples

FIG. 5 shows an example of the carcass cord 10C made up of nine metallicfilaments F which are grouped into four two-filament bunches B1including one waved filament FA and one unwaved filament FB and theremaining one unwaved filament FB which are twisted together at thefinal twist pitch Pc.

FIGS. 6, 7 and 8 show other examples made up of nine, ten and twelvemetallic filaments F, respectively.

In FIG. 6, three three-filament bunches B2 including one waved filamentFA and two unwaved filaments FB are final twisted.

In FIG. 7, two two-filament bunches B1 and two three-filament bunches B2are final twisted.

In FIG. 8, two three-filament bunches B2 including one waved filament FAand two unwaved filaments FB and two three-filament bunches B3 includingtwo waved filaments FA and one unwaved filament FB are final twisted.

As shown in FIGS. 6-8, it is preferable that each bunch B is atwo-filament bunch made up of two filaments F or a three-filament bunchmade up of three filaments F.

It is important to the waved filament FA that the wave pitch Pw is setin a range of from 5.0 to 30.0 times, preferably 10.0 to 25.0 times thediameter (d), and the wave height (h) is set in a range of from 0.5 to4.0 times the diameter (d).

Further, it is preferable to limit the value dXh/Pw within a range offrom 0.014 to 0.028, more preferably 0.020 to 0.025.

In the heavy duty tires for trucks, buses and the like, as the carcasscords, steel cords having a 3+9 structure or 3+9+15 structure have beenwidely used. The above-mentioned metallic cords 10C were designed as asubstitute for such conventional cords. If the diameter (d) is less than0.15 mm, it becomes difficult to provide a strength necessitated by thecarcass of a heavy duty tire. If the diameter (d) is more than 0.30 mm,it becomes difficult to provide flexibility necessitated by the carcassof a heavy duty tire.

If the wave pitch Pw is less than 5.0 times the diameter (d), thestrength of the waved filament liable to decrease. If the wave pitch Pwis less than 30 times the diameter (d), the rubber penetrationdeteriorates.

If the wave height (h) is less than 0.5 times the diameter (d), therubber penetration can not be improved. If the wave height (h) is morethan 4.0 times the diameter (d), the strength of the waved filament isliable to decrease.

Belt Cord Examples

FIG. 9 shows an example of the belt cord 10B composed of nine metallicfilaments F which are grouped into four two-filament bunches B1 of onewaved filament FA and one unwaved filament FB and the remaining oneunwaved filament FB which are twisted at the final twist pitch Pc.

FIGS. 10 and 11 show other examples composed of nine and ten metallicfilaments F, respectively.

In FIG. 10, three three-filament bunches B2 of two waved filament FA andone unwaved filament FB are twisted.

In FIG. 11, three three-filament bunches B3 of one waved filament FA andtwo unwaved filament FB and the remaining one unwaved filament FB aretwisted.

As shown in FIGS. 9-11, it is preferable that each bunch B is atwo-filament bunch or three-filament bunch.

It is important to the waved filament FA that the wave pitch Pw is setin a range of from 5.0 to 30.0 times preferably 10.0 to 25.0 times thediameter (d), and the wave height (h) is set in a range of from 0.2 to3.0 times preferably 0.5 to 2.0 times the diameter (d).

It is preferable to set the value dXh/Pw within a range of from 0.014 to0.028, more preferably 0.020 to 0.025.

These cord structures can be applied to not only heavy duty tires butalso light truck tires.

Hitherto, in the heavy duty tires for trucks, buses and the like, steelcords having a 3+6 structure (two filament diameters) or 2+7 structure(one filament diameter) have been widely used as belt cords. As asubstitute for such conventional cords for heavy duty tires, it ispreferable to set the diameter (d) in a range of from 0.30 to 0.45 mm.

On the other hand, in the light truck tires, steel cords having a 2+6 or3+6 or 2+7 structures have been widely used as the belt cords. As asubstitute for such conventional cords for light truck tires, it ispreferable to set the diameter (d) in a range of from 0.25 to 0.35 mm.

If the diameter (d) is less than 0.25 mm, it becomes difficult toprovide a strength necessitated by the belt. If the diameter (d) is morethan 0.45 mm, it is difficult to prevent the belt rigidity fromexcessively increasing.

If the wave pitch Pw is less than 5.0 times the diameter (d), thestrength of the waved filament liable to decrease. If the wave pitch Pwis less than 30 times the diameter (d), the rubber penetrationdeteriorates.

If the wave height (h) is less than 0.2 times the diameter (d), therubber penetration can not be improved. If the wave height (h) is morethan 3.0 times the diameter (d), the strength of the waved filament isliable to decrease.

In case of the belt cord 10B and the above-mentioned carcass cord 10C,it is preferable that the filament F out of the bunches B (case (ii)) isan unwaved filament FB.

Bead Reinforcing Cord Examples

FIGS. 12 and 13 show examples of the bead reinforcing cord 10A composedof nine and twelve filaments F, respectively.

In FIG. 12, five waved filaments FA and four unwaved filaments FB as abunch are twisted into the cord while interchanging the positions of twofilaments.

In FIG. 13, six waved filaments FA and six unwaved filaments FB as abunch are twisted into the cord while interchanging the positions of twofilaments.

Here, the meaning of the “interchanging the positions of two filaments”is as follows.

When a plurality of filaments, as a single bunch, are twisted, therelative positions of the filaments are substantially not changed alongthe longitudinal direction, and closed spaces are liable to be formedamong the filaments. Such closed spaces can be broken by upsetting thepositional balance of the filaments. In order to effectively upset thepositional balance, the positions of two filaments are intentionallyinterchanged.

The “two filaments” may be specific two filaments, namely, “twofilaments” are the same along the length of the cord. In this case, itcan be said that the cord is formed by final-twisting the first-twisted“two filaments” and the remaining filaments.

It is however, preferable that the “two filaments” are changed along thelongitudinal direction in a predetermined order so as not to concentratethe interchange on specific filaments. For example, provided that thecord is composed of filaments (a), (b), (c), (d), (e), (f) and (g), (aand b) are interchanged in a position, (c and d) are interchanged in asubsequent position, (e and f) are interchanged in a further subsequentposition, (g and a), (b and c), (d and e)—continued. In this case, itmay be said that any two filaments are partially twisted separately fromthe final twist for the cord.

Further, the meaning that “the filaments as a bunch are twisted into thecord” is as follows.

All the filaments are simply gathered as a single bunch, and the bunchis rotated around its axis. This rotation corresponding to theabove-mentioned final-twist. Thus, in the finished cord, each filamentis subjected to a rotation around its axis which is in the samedirection and the same degree as the rotation of the bunch.

In such twist structure, the unity of the filaments F is less incomparison with the carcass cord 10C and belt cord 10B. Therefore, awrapping wire is wound around the filaments F. The winding direction isreverse to the final-twist direction. The winding pitch is set in arange of from 3.0 to 7.0 mm. The diameter of the wrapping wire is set ina range of from 0.13 to 0.17 mm.

In the bead reinforcing cord, the waved filament FA is, before beingtwisted, two-dimensionally waved at wave pitch Pw and wave height (h) soas to be made up of straight segments 13. And all the waved filaments FAhave the same wave height (h) and wave pitch Pw. The wave pitch Pw isset in a range of from 10.0 to 35.0 times the diameter (d). The waveheight (h) is set in a range of from 0.5 to 4.0 times the diameter (d).The value dXh/Pw is set in a range of from 0.014 to 0.028, preferably0.020 to 0.025.

Hitherto, in heavy duty tires for trucks, buses and the like, steelcords having a 3+9 or 3+9+15 structure have been widely used in suchbead reinforcing layer. The above-mentioned metallic cord 10A wasdesigned as a substitute for such conventional cords. If the diameter(d) is less than 0.17 mm, it is difficult to provide a rigiditynecessitated by the bead reinforcing layer, and tire durabilitydecreases. If the diameter (d) is more than 0.25 mm, the beadreinforcing layer loses flexibility and there is a possibility ofseparation failure if the bead portion undergoes excessively largedeformation repeatedly.

If the twist pitch is less than 10 mm, as the initial elongation of thecord increases and it becomes difficult to use in the bead reinforcinglayer. If the twist pitch is more than 30 mm, the cord becomes difficultto handle, and the form stability of the reinforcing layer decreases.

If the wave pitch Pw is less than 10.0 times the diameter (d), thestrength of the waved filament liable to decrease. If the wave pitch Pwis less than 35 times the diameter (d), the rubber penetrationdeteriorates.

If the wave height (h) is less than 0.5 times the diameter (d), therubber penetration can not be improved. If the wave height (h) is morethan 4.0 times the diameter (d), the strength of the waved filament isliable to decrease.

Material of Metallic Filaments

As to the material of the filaments F and wrapping wire W of theabove-mentioned cords 10A, 10B and 10C, hard drawn steel wires whosecarbon content is 0.65 to 0.88 wt % are preferably used. If the carboncontent is less than 0.65 wt %, the strength of the filament tends to beinsufficient. If the carbon content is more than 0.88 wt %, the filamentdecreases in the bending strength.

Further, the metallic filaments F and wrapping wire W are preferablyprovided on the surface with a coat for improving the adhesion to thesurrounding elastomer. For the coat, various resins, metal which actsduring vulcanization and the like can be used.

In the above-mentioned examples of the carcass cord, belt cord and beadreinforcing cord, all the metallic filaments F in each cord have thesame diameter (d).

Comparison Tests

Various experimental steel cords were made, and test tires were madeusing the cords. Then, the following comparison tests were conducted.The test results are shown in Tables 1, 2 and 3.

Test I

Test tires of size 11R22.5 for trucks and buses, having the samestructure except for the carcass cords were made and tested as follows.The carcass was composed of a single ply of cords arranged radially at90 degrees with respect to the tire equator and a cord count of 40/5 cm.The belt was composed of four plies of parallel steel cords having a3+8+13×0.23 conventional structure laid at +65, +20, −20, −20 degreesand a cord count of 20/5 cm.

The test results are shown in Table 1.

Test II

Test tires of two sizes, 11R22.5 for trucks and buses and 205/60R17.5for light trucks having the same structure except for the belt cordswere made and tested as follows.

In case of 11R22.5 heavy duty tire, the carcass was composed of a singleply of steel cords having a 3+9×0.23 conventional structure arranged at90 degrees and a cord count of 35/5 cm. The belt was composed of fourplies of cords laid at +65, +20, −20 and −20 and a cord count of 20/5cm.

In case of 205/60R17.5 light truck tire, the carcass was composed of twoplies of polyester fiber cords having a 1670 dtex/2 structure arrangedat 88 degrees and a cord count of 50/5 cm. The belt was composed of twoplies of cords laid at +18 and −18 degrees and a cord count of 35/5 cm.

The test results are shown in Table 2.

Test III

Test tires of size 11R22.5 for trucks and buses having the samestructure except for the bead reinforcing cords were made and tested asfollows.

The test results are shown in Table 3. In Table 3, item “Filamentrotation”, “S” means that each filament is subjected to a rotation inthe same direction as the twist direction by the twisting. “N” meansthat each filament is not subjected to a rotation by the twistingbecause the filament is rotated in the counter direction duringtwisting.

Test methods and procedures are as follows.

Rubber Penetration Test

The cord was took out from the tire together with the surroundingtopping rubber, and the topping rubber was carefully removed from thesurface of the cord. Then, adjacent two filaments were took outtherefrom along 10 cm long using a knife, and the length of a partsurrounded by the two took-out filaments and the remaining filamentsinto which the rubber completely penetrated was measured to obtain thepercentage of this length to the total length of 10 cm as the rubberpenetration %. Such determination was made on ten positions per tire andthe average thereof was adopted.

Corrosion and Reserved Strength Test

The tire was disassembled after running about 200,000 km, and the steelcords were checked for corrosion. The results are indicated by an indexbased on Ref.1 being 100. The smaller the index, the smaller thecorrosion.

Further, the steel cords were took out and the cord strength wasmeasured. The results are indicated in percentage to the originalstrength.

Bending Rigidity Test

The bending rigidity of the test cord was measured with a V-5 stiffnesstester model 150-D of Taber Industries, U.S.A. as a force in gramcentimeter required to bend the cord 15 degrees.

Shape Retention Test

The cord of 1,000 mm long was coiled into a loop of 200 mm diameter. Theloop was collapsed gradually in fifteen seconds as follows: the loop wasput on a horizontal plane; and one of two oppositely opposed points wasfixed, and the other point is pressed towards the fixed point so thatthe two points contact each other. The collapsed state was maintainedfor ten seconds. Then, the pressing force was decreased gradually infifteen seconds to allow the loop to return to its original shape. Andthe distance L between the two points was measured to obtain the shaperetention rate E=(L/200)×100. The shape retention rate E of each cordwas divided by that of Ex.1 and converted into the reciprocal number andfurther multiplied by 100. The larger the value, the better the shaperetention.

Cord Pull-Out Resistance Test

From the tire, a specimen of the bead reinforcing layer was cut out, anda force required to pull a cord 15 mm out of the specimen was measured.

Strength Diminution Test

Here, the cord strength is shown as a diminution in % of the strength ofthe test cord from that of a standard cord, wherein the standard cordfor each test cord is a compact cord that is the same as the test cordin respect of the material, the number of the filaments, the filamentdiameter, and the final twist pitch, except that all the filaments areunwaved and the first twist pitch is the same as the final twist pitch.Thus, the smaller the value, the higher the strength.

From the test results, it was confirmed that although the cord diameteris decreased, rubber penetration, strength, initial elongation and thelike can be improved.

Further, as shown in FIG. 14 which shows the strength diminution andrubber penetration as a function of the value of dXh/Pw, by setting thedXh/Pw value in a range of 0.014 to 0.028, both of the rubberpenetration and the rate of diminution of the cord strength can bemaintained in a good level.

The present invention can be suitably applied to not only heavy dutytires but also light truck tires, passenger car tires and the like.

TABLE 1 Tire Ref.1 Ref.2 Ref.3 Ref.4 Ex.1 Ex.2 Ex.3 Ex.4 Cord structure1X9X0.20 1X9X0.20 1X9X0.20 1X9X0.20 1X9X0.20 1X9X0.20 1X9X0.20 1X12X0.15Carbon content (%) 0.82 0.82 0.82 0.82 0.82 0.82 0.82 0.82 Twist pitchPc (mm) 17 17 17 17 17 17 17 15 Bunch 1 Twist pitch Pf 0 0 0 0 10XPc10XPc 10XPc 7XPc No. of filaments Waved 0 3(A:A:A) 3(A:A:A) 2(A:A)2(A:B) 1(A) 2(A:A) 2(A:B) Unwaved 9 0 0 1 1 2 1 2 Bunch 2 Twist pitch Pf0 0 0 0 10XPc 10XPc 10XPc 7XPc No. of filaments Waved 3(A:A:A) 3(A:A:A)2(A:A) 2(A:B) 1(A) 2(A:A) 2(A:B) Unwaved 0 0 1 1 2 1 2 Bunch 3 Twistpitch Pf 0 0 0 0 10XPc 10XPc 10XPc 7XPc No. of filaments Waved 3(A:A:A)3(A:A:A) 2(A:A) 2(A:B) 1(A) 2(A:A) 2(A:B) Unwaved 0 0 1 1 2 1 2 Wave A AA A:B A A A:B Pitch Pw (mm) 10 5 10 5.0:3.0 5 4 2.0:4.0 Height h (mm)0.5 1 1 0.45 0.5 0.5 0.4 Cord characteristics Cord diameter (mm) 0.710.85 0.83 0.82 0.75 0.73 0.75 0.78 Strength (N/sq.mm) 3052 2980 29903000 3020 3030 3025 3010 Strength diminution (%) 0.2 2.2 2.3 2 1 1.2 1.22 Elongation (%) @ 50N 0.107 0.125 0.128 0.108 0.108 0.107 0.108 0.109Bending rigidity (gf.cm) 23 20 20 21 21 22 21 20 Rubber penetration (%)0 78 77 82 98 95 96 95 Corrosion (index) 100 55 53 45 11 20 18 25Reserved strength (index) 88 92 93 95 92 95 93 91

TABLE 2 Tire Ref.1 Ref.2 Ref.3 Ref.4 Ref.5 Ex.1 Ex.2 Ex.3 Ex.4 Ex.5 Tiresize 11R22.5 11R22.5 11R22.5 11R22.5 205/60R17.5 11R22.5 11R22.5 11R22.5205/60R17.5 205/60R17.5 Cord structure 1X9X0.38 1X9X0.38 1X9X0.381X9X0.38 1X9X0.30 1X9X0.38 1X9X0.38 1X9X0.38 1X9X0.30 1X7X0.25 Carboncontent (%) 0.82 0.82 0.82 0.82 0.82 0.82 0.82 0.82 0.82 0.82 Twistpitch PC (mm) 18 18 18 7 18 18 18 18 18 18 Bunch 1 Twist pitch Pf 0 0 00 0 10XPc 10XPc 10XPc 10XPc 10XPc No. of fila- 0 3(A;A;A) 3(A;B;C)2(A;B) 3(A;A;A) 2(A;B) 2(A;A) 1(A) 2(A;B) 2(A;A) ments Waved Unwaved 9 00 1 0 1 1 2 1 1 Bunch 2 Twist pitch Pf 0 0 0 0 0 10XPc 10XPc 10XPc 10XPc10XPc No. of fila- 3(A;A;A) 3(A;B;C) 2(A;B) 3(A;A;A) 2(A;B) 2(A;A) 1(A)2(A;B) 2(A;A) ments Waved Unwaved 0 0 1 0 1 1 2 1 1 Bunch 3 Twist pitchPf 0 0 0 0 0 10XPc 10XPc 10XPc 10XPc 10XPc No. of fila- 3(A;A;A)3(A;B;C) 2(A;B) 3(A;A;A) 2(A;B) 2(A;A) 1(A) 2(A;B) 0 ments Waved Unwaved0 0 1 0 1 1 2 1 1 Wave A A;B;C A;B A A;B A A A;B A Pitch Pw(mm) 53.0;5.0;6.3 1.0;15 5 5.0;6.3 5 5 5.0;6.3 5 Height h (mm) 0.25 0.25;0.25;0.25 0.25 0.25;0.34 0.25 0.25 0.25 0.25 0.34 Cord characteristics Corddiameter (mm) 1.4 1.5 1.56 1.48 1.52 1.48 1.5 1.45 1.15 0.78 Strength(N/sq.mm) 3013 2980 2978 3000 2980 3021 3025 3030 3035 3009 Strengthdiminution 0 2.9 3 2.5 2.9 2.5 2.5 2.2 2.6 2.7 (%) Elongation (%) @0.052 0.069 0.065 0.012 0.089 0.012 0.012 0.002 0.015 0.013 50N bendingrigidity 260 220 215 232 91 232 231 235 96 28 (gf.cm) Rubber penetration0 91 93 92 91 97 95 95 96 93 (%) Corrosion (index) 100 86 89 90 86 8 1015 9 13 Reserved strength 86 96 96 95 95 95 95 95 93 93 (index)

TABLE 3 Tire Ref.1 Ref.2 Ref.3 Ref.4 Ref.5 Ref.6 Cord structure1X7X0.23+ 1X7X0.23+ 1X7X0.23+ 1X9X0.20+ 1X9X0.20+ 1X9X0.20+ 1X0.151X0.15 1X0.15 1X0.15 1X0.15 1X0.15 Carbon content (%) 0.82 0.82 0.820.82 0.82 0.82 Twist pitch (mm) 15 15 15 18 18 18 Filament rotation N NS N N S No. of filaments Waved 0 3 7 0 3 9 Unwaved 7 4 0 9 6 0 Wave 2-D2-D 2-D 2-D Height h (mm) 0.1 0.3 1.5 0.45 Pitch Pw (mm) 2 3.3 10 5dXh/Pw 0.012 0.021 0.03 0.018 Wrapping wire Dia. (mm) 0.15 0.15 0.150.15 0.15 0.15 Winding pitch (mm) 5 5 5 5 5 5 Cord characteristics Corddiameter (mm) 0.7 0.82 0.8 1.1 1.23 1.19 Strength (N/sq.mm) 3010 29802930 3035 3010 2980 Strength diminution (%) 0 1.9 3.1 0 2.5 3.2Elongation (%) @ 50N 0.118 0.12 0.148 0.119 0.121 0.152 Bending rigidity(gf.cm) 29 27 24 33 31 29 Rubber penetration (%) 0 91 95 0 92 94Corrosion (index) 100 20 18 100 23 20 Reserved strength (%) 89 95 97 8594 95 Shape retention (index) 95 99 101 95 100 101 Pull-out resistance(N/15 mm) 135 181 192 128 173 177 (broken) (broken) (broken) (broken)Tire Ex.1 Ex.2 Ex.3 Ex.4 Cord structure 1X7X0.23+ 1X7X0.23+ 1X9X0.20+1X9X0.20+ 1X0.15 1X015 1X0.15 1X015 Carbon content (%) 0.82 0.82 0.820.82 Twist pitch (mm) 15 15 18 18 Filament rotation S S S S No. offilaments Waved 3 4 3 5 Unwaved 4 3 6 4 Wave 2-D 2-D 2-D 2-D Height h(mm) 0.3 0.45 0.45 0.5 Pitch Pw (mm) 3.3 4.5 5 0.45 dXh/Pw 0.021 0.0230.018 0.022 Wrapping wire Dia. (mm) 0.15 0.15 0.15 0.15 Winding pitch(mm) 5 5 5 5 Cord characteristics Cord diameter (mm) 0.78 0.8 1.21 1.28Strength (N/sq.mm) 2950 2920 3010 2980 Strength diminution (%) 2.1 2.8 22.7 Elongation (%) @ 50N 0.12 0.122 0.121 0.123 Bending rigidity (gf.cm)28 27 31 30 Rubber penetration (%) 97 98 96 95 Corrosion (index) 11 1512 14 Reserved strength (%) 96 97 95 97 Shape retention (index) 100 101102 103 Pull-out resistance (N/15 mm) 191 195 181 185 (broken) (broken)(broken) (broken)

What is claimed is:
 1. A pneumatic tire comprising: a belt disposedradially outside a carcass in a tread portion, said belt being beingmade of belt cords, each said belt cord being made up of 6-10 metallicfilaments whose diameter is in a range of from 0.25-0.45 mm, said 6-10metallic filaments being grouped into a plurality of elements, saidplurality of elements being (i) bunches of 2 or 3 or 4 filaments, or(ii) 1 filament and bunches of 2 or 3 or 4 filaments, wherein each ofthe bunches includes at least one waved filament and at least oneunwaved filament, and the bunches comprising a bunch including pluralkinds of waved filaments having different wave pitches, the wavedfilament being two-dimensionally waved at a wave pitch and a wave heightbefore twisted, wherein the wave pitch is in a range of from 5.0 to 30.0times the diameter of the filament, and the wave height is in a range offrom 0.2 to 3.0 times the diameter of the filament, said plurality ofelements being twisted together into the cord at a twist pich of from10-40 mm so that the two-dimensionally waved filaments are eachsubjected to a certain rotation around its axis.
 2. The pneumatic tireaccording to claim 1, wherein the filaments in each said bunch aretwisted at a twist pitch Pf of from 3 to 20 times the twist pitch Pc. 3.The pneumatic tire according to claim 1, wherein the diameter is in arange of from 0.25 to 0.35 mm.
 4. The pneumatic tire according to claim1, wherein the diameter is in the range of from 0.30 to 0.45 mm.
 5. Thepneumatic tire according to claim 1, further comprising a beadreinforcing layer disposed in a bead portion, said bead reinforcinglayer being made of bead reinforcing cords, each said bead reinforcingcord being made up of 7 to 12 metallic filaments whose diameter is in arange of from 0.17 to 0.25 mm and a wrapping wire wound around thefilaments and having a diameter in a range of from 0.13 to 0.17 mm, saidmetallic filaments including at least two waved filaments and at leastthree unwaved filaments, the waved filament being two-dimensionallywaved before being twisted so as to be made up of straight segments in azigzag formation, all the waved filaments having the same wave pitch andthe same wave height, the wave pitch being in a range of from 10.0 to35.0 times the diameter of the filament, and the wave height being in arange of from 0.5 to 4.0 times the diameter of the filament, and thevalue dXh/Pw is in a range of from 0.0 14 to 0.028, said 7 to 12metallic filaments being twisted at a twist pitch of from 10 to 30 mmwhile interchanging at least two of said seven to twelve metallicfilaments in their relative positions, the wrapping wire being woundaround the twisted filaments in a direction reverse to said twistdirection at a winding pitch of 3.0 to 7.0 mm.